This invention relates to nuclear thermionic converter power sources, and more particularly to a control system therefor.
One type of nuclear reactor system which is useful in space vehicles includes an array of units that contain quantities of nuclear fuel and thermionic converters. The fuel heats the emitter of each thermionic converter while a cooling fluid cools the collector, and the temperature difference results in the production of electricity. The electrical load which is connected to the converter outputs sometimes changes rapidly to very different levels. This can lead to wide fluctuations in the voltage supplied to the loads and to wide fluctuations in the temperature of the thermionic emitters, both of which are highly undesirable. Variations in voltage are, of course, undesirable in that they can interfere with proper orientation of equipment energized by the reactor system. Variations in emitter temperature are undesirable because they seriously reduce the lift of the emitters.
Various control systems can be used to govern the operation of the reactor. One possible control scheme is to use dummy loads that are connected or disconnected to compensate for sudden change in real loads, so the reactor always operates at a predetermined point that avoids temperature or voltage fluctuations. However, this requires operation at a maximum neutron flux which reduces the life of the nuclear fuel. Another control scheme involves the comparison of the converter output voltage to a predetermined constant voltage, and the regulation of neutron flux to maintain a constant voltage. While this produces voltage regulation, it results in temperature fluctuations with load, which decreases the life of the thermionic emitters. Still another control scheme involves the use of a variable gain power regulator between the thermionic converters and the load to vary the load voltage, wherein the voltage gain of the regulator is adjusted as a function of thermionic current and neutron flux. Any deviation of the output voltage from a predetermined level is used to control the neutron flux in a direction to reduce the deviation. This system minimizes temperature fluctuations, but results in brief but large fluctuations in output voltage to the load when the load changes suddenly. A control system that minimized both emitter temperature fluctuations and load voltage fluctuations in spite of sudden changes in load would permit the reactor system to operate reliably over long periods while promoting proper operation of the loads.